FI103812B - Carbodiimide-modified polyester fibers and a process for their preparation - Google Patents

Abstract

There are described polyester fibres and filaments which, as a result of a reaction with carbodiimides, have capped carboxyl end groups, for which   - the capping of the carboxyl end groups was effected predominantly by reaction with mono- and/or biscarbodiimides from which, however, only less than 30 ppm (by weight) of the polyester are left in free form in the fibres and filaments,   - the free carboxyl end group content is less than 3 meq/kg of polyester, and   - the fibres and filaments still contain at least 0.05 per cent by weight of at least one free polycarbodiimide or a reaction product with still reactive carbodiimide groups, and a process for preparing them. <??>The filaments described are suitable in particular for manufacturing paper machine wire-cloths.

Description

Carbodiimide-Modified Polyester Fibers and Process for Their Manufacture 103812

The invention relates to chemical polyester fibers, mainly polyester monophilic fibers, stabilized against thermal decomposition, and in particular to hydrolytic decomposition by adding a combination of mono- and polycarbodiimides, and also to suitable methods for their preparation.

Polyester molecules are known to cleave under thermal stress such that, for example, upon opening of the ester bond of polyethylene terephthalate, a carboxyl end group and a vinyl ester are formed, whereupon the vinyl ester further reacts with acetaldehyde. This type of thermal disturbance is primarily influenced by the reaction temperature, the time of action, and possibly the nature of the polycondensation catalyst.

In contrast, the resistance to hydrolysis of polyester is strongly dependent on the number of carboxyl end groups per 20 weight units. It is known that the hydrolysis resistance can be improved by trapping these carboxyl end groups by chemical exchange reactions. Such "blocking" of carboxyl end groups has already been suggested by a number of exchange reactions with aliphatic, aromatic but also cycloaliphatic mono-, bis- or polycarbodiimides *.

Thus, for example, DE-OS 1770495 describes stabilized polyethylene glycol terephthalates obtained by the addition of polycarbodiimide. Due to the slow reaction rate generally observed in the case of polycarbodiimides, it is necessary to take care of the longer residence time of the polycarbodiimide in the polyester melt. For this reason, polycarbodiimides were already added in the polycondensation reaction of the polyesters. However, such a measure-35 has many disadvantages. For example, because of the long reaction time, many by-products are formed, possibly the actual polyester polycondensation reaction is also prevented.

In contrast, it is known that monocarbodiimides and biscarbodiimides react much faster with polyester crosslinking agent. Therefore, it is possible to reduce the time required for mixing and reaction so that these raw materials can be added together with meltable polyester granules immediately prior to introduction into the spinning extruder. An example of the addition of biscarbodiimides for this purpose is DE-OS 2020330, the addition of monocarbodiimides is DE-AS 2458701 and JA AS 1-15604 / 89.

Both of these latter publications are directed specifically to the production of stabilized polyester filaments, in which case it is recommended to leave a small excess of carbodiimide in the finished yarn. According to the examples in DE-AS 2458701, the excess in stoichiometric amount required should be up to 7.5 to 20 mval per kg of polyester, while JA-AS 1-15604 / 89 requires 0.005 to 1.5% by weight. excess monocarbodiimide specifically recommended therein. In both cases, when calculating the amounts required for stoichiometry, it is taken into account that during the melting of the polymer to be spun, a few additional carboxyl groups are formed which must likewise be prevented. As can be seen in particular from JP-AS 1-15604 / 89, for the desired thermal and hydrolytic resistance of the yarns produced therein, it is of particular importance that the finished yarns or monofilaments still contain free carbodiimide, since otherwise, for example, under these circumstances such raw materials would soon be unusable. JP-AS further shows that the addition of polycarbodiimides does not correspond to the 35 prior art.

103812 3

The drawback of all known processes using excess mono- or bis-carbodiimides is that due to the non-negligible evaporation of these products, and in particular from the thermally and hydrolytically produced degradation products, such as the corresponding isocyanates and aromatic amines, and significant environmental load. The use of stabilized polyester yarns is due to their special properties, usually at high temperatures and generally in the presence of water vapor. Under these conditions, such loading is expected from the additional addition of carbodiimide and its derivatives. Due to their volatility, it is expected that these compounds may be diffused from the polyester or also extracted, for example, with solvents or mineral oils. Therefore, sufficient storage effect is not guaranteed over time.

At this technical level, it was still the task of inventing the stabilization of polyester filaments to minimize all possible carboxyl end groups on the one hand and, on the other hand, to minimize the load caused by volatile mono or biscarbodiimides and their derivatives.

·· 25 It was surprisingly found that this problem can be solved by using mixtures of certain carbodiimides. Therefore, the invention relates to such polyester fibers and filaments in which the inhibition of the carboxyl end groups is accomplished by essentially reacting these carboxyl end groups with the mono and / or biscarbodiimides, but the fibers and filaments of the invention contain very small amounts. or not at all free of these carbodiimides. On the contrary, it is necessary that the polyester fibers and filaments contain at least 0.05% by weight of at least 10,103,812% of at least one polycarbodiimide, in which case this polyester must be free or have at least a few reactive carbodiimide groups. Desired polyester fibers and filaments having 5 significantly improved thermal and / or hydrolytic degradation resistance should contain less than 3 mval / kg carboxyl end groups in the polyester. Preferred are fibers and filaments in which the number of carboxyl end groups is reduced to less than 2, preferably 10 to less than 1.5 mval / kg of polyester. It is preferred that the amount of free mono- and / or bis-carbodiimides is from 0 to 20, in particular from 0 to 10 parts per million by weight of the polyester.

Thus, care must be taken that the fibers and filaments still contain polycarbodiimides or their reaction products, which still have reactive groups. Preferably the concentrations are in the range of 0.1 to 0.6, especially 0.3 to 0.5% by weight of polycarbodiimide in the polyester fibers or filaments. A suitable carbodiimide has a molecular weight of 2000-15000, preferably 5000 to about 10,000.

For the production of high performance fibers, the use of high molecular weight polyesters having a minimum intrinsic viscosity of 0.64 (dl / g) is required. Measurements were made in dichloroacetic acid at 25 ° C. The process for the preparation of claimed stabilized polyester 25 fibers and filaments according to the invention comprises adding an amount of mono- and / or bicarbodiimide corresponding to at most the stoichiometric amount based on the number of carboxyl groups, and additionally at least 0.15% by weight of polycarbonate. bodimide addition based on polyester. This mixture of polyester and carbodiimides is further spun and further processed into yarns, monofilaments or staple fibers. In order to achieve particularly low values for free mono- and / or biscarbodiimide, it is preferable to add less than 90% of the stoichiometrically required amount, preferably up to only 50-85% of this amount of mono- and / or biscarbodiimide. Stoichiometric amount refers to the amount in milliequivalents per unit weight of polyester that can and should react with the carboxyl groups at the end of the polyester. Further, when calculating the amount required for stoichiometry, it should be noted that, in general, additional carboxyl end groups are formed at the thermal load, for example represented by the melting of the polyester. These carboxyl terminal groups, which are additionally formed during the melting of the polyester raw material used, must also be taken into account when calculating the amount of carbodiimide required by stoichiometry.

According to the present invention, it is preferable to use as a spinning material polyesters which, by their very nature, contain little carboxyl end groups. This can be achieved, for example, by using the so-called solid condensation method. It was found that the polyester used should contain less than 20, preferably even less than 10 mval carboxyl-head-20 groups per kilogram. These values already take into account the increase in smelting.

Polyesters and carbodiimides are preferably not stored at high temperatures for long periods. More distantly, it has already been mentioned that during melting, polyesters form more carboxyl end groups. Also, the used carbodiimides can decompose at high temperatures in the polyester melt. Therefore, it is desirable to limit the contact or reaction time of the carbodiimide additions to the molten polyester as short as possible. When using a die extruder-30, it is possible to reduce the residence time in the molten state to less than 5, preferably less than 3 minutes. The thawing time in the extruder can only be limited so that sufficient mixing of the reactants is a prerequisite for the proper reaction between the carbodiimide and the polyester carboxyl end groups. This can be achieved by a corresponding design of the extruder or, for example, by the use of static mixers.

In principle, all fiber-forming polyesters, i. aliphatic / aromatic polyesters such as polyethylene terephthalates or polybutylene terephthalates, but also fully aromatic and e.g. halogenated polyesters can be used in the same way. Preferred structural members of the fiber-forming polyesters are diols and dicarboxylic acids or oxycarboxylic acids formed respectively. The main acid moiety of the polyester is terephthalic acid, of course other suitable compounds, especially para or trans, such as 2,6-naphthalene-dicarboxylic acid, but also p-hydroxybenzoic acid. Typical suitable divalent alcohols would be, for example, ethylene glycol, propanediol, 1,4-butanediol as well as hydroquinone, etc. Preferred aliphatic diols have from two to four C atoms. Of particular preference is given to ethylene glycol. Long chain diodes may be used in amounts of up to about 20 mol%, preferably less than 10 mol%, to modify the properties.

However, high molecular weight polymers of pure polyethylene terephthalate and their copolymerates with minor amounts of comonomers have proven to be suitable for special technical purposes, provided that the thermal load is generally suitable for the properties of the polyethylene terephthalate. In the other 30 cases, suitable known full aromatic polyesters must be avoided.

Particularly preferred are therefore the polyester fibers and filaments according to the invention which consist predominantly or wholly of polyethylene terephthalate 35, and in particular those having a molecular weight of at least 0.64 (dl / g), preferably at least 0.70 (dl). / g). The intrinsic viscosity values are determined in dichloroacetic acid at 25 ° C. Stabilization of the filaments or fibers of the invention is achieved by the addition of a combination of mono- and / or biscarbodiimide on the one hand and a combination of polymeric carbodiimide on the other hand. The use of mono-carbodiimides is advantageous because they are particularly good because of their high reaction rate in the exchange reaction of the carboxyl end groups of the polyester. However, if desired, they may be partially or completely replaced by corresponding amounts of biscarbodiimide in order to take advantage of the already very low evaporation of these compounds. In this case, however, care must be taken to ensure that a sufficiently long contact time is selected so that, even when using kar-15 bodimide in a disk extruder, a sufficient reaction is obtained to ensure adequate mixing.

After the polycondensation, the carboxyl groups remaining in the polyester according to the process of the invention must be prevented by reacting them predominantly with mono-20 or bis-carbodiimide. A small proportion of the carboxyl end groups under these conditions of the invention also react with the carbodiimide groups derived from the polycarbodiimide used.

Therefore, the polyester fibers and filaments of the invention contain essentially the reaction products of the carboxylimides used instead of the carboxyl end groups. Mono- or bis-carbodiimides, which are allowed very little, if at all, to be free of fibers and filaments, are known aryl, alkyl and cycloalkylcarbodiimides. The aryl nuclei of the diarylcarbodiimides preferably used may be unsubstituted. However, aromatic carbodiimides substituted at the 2- or 2,6-position and thus sterically hindered are used predominantly. Already 35 DE-AS 1494009 lists a large number of mono- 8 103812 carbodiimides with sterically hindered carbodiimide groups. For example, N, N '- (di-o-tolyl) carbodiimide and N, N' - (2,6,2 ', 6'-tetraisopropyl) diphenylcarbodiimide are, for example, mono-carbodiimides.

Suitable biscarbodiimides according to the invention are described, for example, in DE-OS 2020330.

Suitable polycarbodiimides are those compounds of the invention wherein the carbodiimide units are bonded to each other via mono- or di-substituted aryl backbones, wherein the aryl backbones are phenyls, naphthyls, diphenyls and divalent substituent and divalent substituents and diphenylmethane substituents. substituents of monodiarylcarbodiimides substituted on the aryl backbone.

A highly preferred polycarbodiimide is a standard commercial aromatic polycarbodiimide substituted with isopropyl groups at the o-position with respect to the carbodiimide groups, i.e.. 2,6-position or 2,4,6-position of the benzene backbone.

Preferably, the free or bonded polycarbodiimides in the polyester filaments of the invention have an average molecular weight of 2000 to 15000, in particular 5000 to 10000. As noted above, these polycarbodiimides react significantly more slowly with carboxyl end groups. In the case of such a reaction, it is preferable to initially allow one carbodiimide group to react. However, the other groups present in the polymeric carbodiimide result in the desired storage effect and result in substantially improved stability of the resulting fibers and filaments. It is crucial for the desired heat resistance, and especially for the hydrolytic resistance, of the formed polyester mass that not all of the polymeric carbodiimides therein are reacted but that there are still free carbodiimide groups present to bind more carboxyl end groups.

The polyester fibers and fibers produced according to the invention may contain common additives such as titanium dioxide as a dimming agent or additives for example to promote dyeing or to reduce static electricity. Similarly, additives or comonomers which are known to reduce the flammability of the fibers and filaments produced are, of course, also suitable.

The polyester melt may also be blended or may already contain, for example, colored pigments, soot or soluble dyes. By mixing with other polymers, such as polyolefins, polyesters, polyamides or polytetrafluoroethylenes, completely new textile effects may possibly be achieved. Also, the addition of cross-linking agents and similar additives can bring benefits to selected uses.

As stated above, mixing and melting are required to make the polyester fibers and filaments of the invention. Preferably, this thawing can be performed in a disk die extruder just before the actual spinning. The addition of carbodiimides ··· can be accomplished by blending into a plurality of polyester fibers, impregnating the polyester material with suitable carbodiimide solutions prior to the extruder, but also by immersion or the like. Another method of addition particularly suited for the administration of polymeric carbodiimides is the preparation of master batches in polyester. Using these concentrates, the polyester material to be treated can be blended directly before the extruder or, for example, using a twin-screw extruder can also be blended in the extruder. If the spun polyester-35 material is not in the form of chips but has been supplied as a fluid melt, for example, the corresponding Dispensing Devices will naturally have to be considered for the carbodiimide which may be melted.

The amount of monocarbodiimide to be added will depend on the carboxyl end group of the starting material polyester, taking into account further carboxyl end groups likely to be formed during the melting process. In order to minimize the burden on the environment and the workforce, it is preferable to work with 10 sub-cubic meters of mono- or bis-carbodiimide. Preferably, the amount of mono- or bis-carbodiimide added should be less than 90% of the calculated stoichiometric amount, in particular 50-85% of the stoichiometric amount of mono- or bis-carbodiimide corresponding to the carbocyl end group. Here, care must be taken to ensure that premature evaporation of used mono- or bis-carbodiimides does not cause losses. A preferred way of adding polycarbodiimide is by adding base batches containing a higher percentage, for example 15% polycarbodiimide, as a standard polymeric polyester granulate.

Once again, particular mention should be made of the risk of side reactions occurring during the common melting step under thermal loading for both the polyesters and the carbodiimides used. Therefore, the residence time of the carbodiimides in the melt should preferably be less than 5 minutes, especially less than 3 minutes. Under these conditions, when the amounts of the mono- or bis-carbodiimide used are well mixed, they react almost quantitatively, i. they cannot subsequently be shown to be 30 free in extruded yarns. In addition, a small, albeit very small percentage of the carbodiimide groups of the polycarbodiimide used still respond, but are primarily responsible for the storage function. This operation has for the first time 35 enabled the production of polyester fibrils and filaments which are effectively protected against thermal, in particular hydrolytic, degradation, and which contain virtually no free mono- or biscarbodiimide and only very small amounts of their degradation. or seu-5 beach products that would burden or pollute the environment. The presence of polymeric carbodiimides achieves the desired long-term stability of the polyester material so treated. It is surprising that this property reliably monitors the polycarbodiimides, although attempts at stabilization using these compounds alone have not resulted in the required stability.

The use of polymeric carbodiimides to achieve long-term stability, in addition to low thermal degradation and low evaporation of these compounds, also provides substantially greater certainty in the toxicological sense. This is especially true of all polymer molecules of polycarbodiimides which are already chemically bonded to the polyester material by at least one carbodiimide group via the carboxyl terminus group of the polyester.

Examples

The following examples are provided to illustrate the invention. In all examples, a dried, solid-condensed polyester granulate with an average carboxyl end group content of 5 mval / kg polymer was used. The monomeric carbodiimide was N, N'-2,2 ', 6,6'-tetraisopropyldiphenylcarbodiimide. The polymeric carbo-30-diimide used in the following experiments was an aromatic polycarbodiimide which, at the - · o-positions, m.p. The 2,6- or 2,4,6-positions had a benzene backbone substituted with isopropyl groups. It was not used as a pure mixture but as a base mixture (15% polycarbodiimide in polyethylene terephthalate (commercial product R Stabaxol KE 35 7646, Rhein-Chemie, Rheinhausen, Deutschland).

12 103812

The mixing of the carbodiimide with the masterbatch and the polymeric material took place in the tank by mechanical shaking and stirring. Immediately thereafter, this mixture was transferred to a single-screw extruder, manufactured by Reifenhäuser, Deutschland, Type S 45 A. The temperature of the separate extruder zones was 282-293 ° C, the extruder being run at 500 g molten mass / minute using conventional monofilament spun extruders. The residence time of the mixture in the molten state was 2.5 minutes. The newly-spun monofilaments, after a short airspace, were introduced into a water bath, after which they were continuously stretched in two steps. The stretch ratio in all experiments was 1: 4.3. The temperature of the first stage of the stretching was 80 ° C and of the second stage 90 ° C, while the spinning yarns had an advance speed of 32 m / min when leaving the stretch bath. Immediately thereafter, heat fixation was performed in a fixation channel at 275 ° C. The final diameter of all spun monofilaments was 0.4 mm. As a stability test, the tensile strength (tensile strength) of the resulting monofilaments was first tested immediately after production and secondly after storage of the monofilaments at 135 ° C in a water-vapor atmosphere for 20 hours. The tensile strength was then re-determined and the ratio of the residual tear strength to 25 and the original tensile strength was calculated. It is a measure of the stability effect achieved by the additions.

Example 1 In this example, the monofilaments were spun without any addition. Of course, in the experiments obtained, no free monocarbodiimide was found, with a carboxyl end group concentration of 6.4 mval / kg of polymer. The following table summarizes the experimental conditions and the results obtained.

»103812

Example 2 This example was also made as a comparison. However, under conditions similar to Example 1, a monophile was again prepared using only 0.6% by weight of N, N1-5 (2,6,2 ', 6'-tetraisopropyldiphenyl) carbodiimide as a blocking agent for the carboxyl groups. This 0.6 wt.% Corresponds to 16.6 mval / kg, thus working with an excess of 10.2 mval / kg of polymer. Under these conditions, a polyester monophile is obtained which has very good stability against thermal and hydrolytic stress. However, the drawback is that the finished products have a free monocarbodiimide content of 222 parts per million.

Example 3 Example 1 was repeated here as a comparison. However, this time, 0.876% by weight of the above polycarbodiimide was added, now 15% as a masterbatch. This experiment was performed once more to verify the literature that even in the presence of a significant excess of polycarbodiimide, probably due to the low reactivity, reduced thermal and hydrolytic resistance to the state of the art could be observed. This example clearly shows this to be the case. Interestingly, this amount of polycarbodiimide already selected appears to result in a significant crosslinking of the polyester, which can be inferred from the marked increase in intrinsic viscosity values. Generally, this kind of crosslinking of yarn-forming polymers can only be allowed within narrow limits if it is accurately reproducible and no difficulty in spinning or stretching the yarn formed therefrom is expected.

* - · Example 4

The procedure of Example 1 or Example 2 was repeated, although now amounts of monocarbodiimide corresponding to a stoichiometric value or 35 to 20% excess of monocarbodiimide were added. Again, the results obtained are shown in the table below. In run 4a, the required amount of monocarbodiimide was added in a stoichiometric manner, while in run 4b an excess of 1.3 mval / kg of monocarbodiimide was added. As shown in the table, the relative residual strengths obtained after 80 hours of steam treatment at 135 ° C do not correspond to the prior art. Also, an excess of about 20%, as can already be deduced from the numerical values of DE-AS 24 58 701, for example, does not yet result in high hydrolytic durability as can be achieved, for example, in the prior art. However, this means that according to the prior art, only a significant excess of monocarbodiimide could achieve particularly good relative residual strength after thermal hydrolytic stress. This is necessarily accompanied by a high concentration of free monocarbon diimide.

Example 5

Example 1 was repeated this time, however, with polycarbodiimide in addition to monocarbodiimide 20 according to the invention. In run 5a, the amount of monocarbodiimide added was only 5.5 mval / kg, i.e. worked with a 0.9 mval / kg deficit calculated stoichiometrically. As a percentage, this is a 14.1% deficit or only 85.9% of the stoichiometric requirement was dispensed. As can be seen from the table, the concentration of free monocarbodiimide is within the desired range, but especially the thermal and hydrolytic resistance within the error limits is without doubt comparable to the best compositions so far. The observed deviations do not significantly differ from the value of the pre-30 in Example 2 or Example 6. Example 5 was repeated, run 5b this time, using exactly the equivalent amount of monocarbodiimide and the addition of polycarbodiimide at the appropriate concentration limits. Increasing the monocarbodiimide concentration did not affect the relative residual strength of 103812 obtained. Only a slight increase in free monocarbodiimide was observed.

Example 6

However, work was carried out in accordance with Example 5 at this time using 1.3 mval / kg of monocarbodiimide in excess, or 20% more than stoichiometrically required. A similar excess was already used in run 4b. Under the operating conditions selected, this amount alone proves to produce an undesirable high concentration of 33 ppm free monocarbodiimide, p. significantly more than was observed in time 5a and 5b. Such a value should not really be allowed anymore, since it was shown in the time of Example 5 that the same relative residual strength, i.e. the same thermal-hydrolytic resistance can be achieved with a much lower amount of free monocarbodiimide and thus also with a lower environmental load. Exceeding the set limit of 30 parts per million of free monocarbodiimide is of course of minor importance here.

An excess of 1.3 mval / kg of monocarbodiimide results in only 10% of the limit set for free monocarbodiimide content under the selected 20 experimental conditions. This slight overshoot may further add to the perception that, under the selected experimental conditions, the apparently small amount of monocarbodiimide is degraded or evaporated. Thus, a slight excess of the stoichiometric amount may be allowed in single cases, however, within the selected limits of a maximum of 30 ppm free monocarbodiimide / kg of polymer.

It should be noted that here too, an additional dose of polycarbodiimide 30, as compared to Example 4, clearly can still * - * improve the relative residual strength.

The following table summarizes the experimental results and reaction conditions. The addition of monocarbodiimide is first expressed in weight percent and then in the second sa-35 granule as mval / kg. The next column gives an aliquot or excess of monocarbodiimide, calculated by stoichiometry, followed by the polycarbodiimide percentage by weight. The following columns give measurement results for the monofilaments obtained, each having a diameter of 0.40 mm. Next, the number of carboxyl end groups in mval / kg, then the amount of free carbodiimide in parts per million (by weight) is reported. The free carbodiimide content was determined by extraction and gas chromatographic analysis according to JP-AS 1-15604-89. Then follow the columns showing the residual strength and intrinsic viscosity of the individual wire tests.

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Claims (17)

1. Polyester fibers and filaments which, by reaction with carbodiimides, exhibit closed carboxyl end groups, characterized in that - the closure of the carboxyl end groups is effected mainly by reacting them with mono- and / or biscarbodiimides which are contained in however, the free form in the fibers and filaments is longer only in an amount less than 30 ppm 10 (wt) of the polyester; free polycarbodiimide or a reaction product containing reactable carbodiimide groups. Fibers and filaments according to claim 1, characterized in that the content of free mono- and / or biscarbodiimides is 0-20, preferably 1-10 ppm (weight) of the polyester. Fibers and filaments according to claim 1 or 2, characterized in that the amount of free carboxyl end groups is less than 2, preferably less than 1.5 mw / kg polyester. * 25 4. Fibers and filaments according to any of the preceding claims, characterized in that the content of at least one polycarbodiimide or reaction product containing still reactable carbi-diimide groups is 0.1-0.6, preferably 0.3-0.5. 30% by weight. 5. Fibers and filaments according to any of the preceding claims, characterized in that the yarn forming polyester has an average molecular weight corresponding to at least an intrinsic viscosity of 0.64 (dl / g) measured in dichloroacetic acid at 25 ° C. 103812 Fibers and filaments according to any of the preceding claims, characterized in that the average molecular weight of the polycarbodiimide (poycarbodiimides) used is about 2000-15000, preferably of 5000-10000. Fibers and filaments according to any one of claims 1-6, characterized in that they consist of monofiles with a circular or profiled cross section and their - possibly equivalent - diameter is 0.1 - 2.0 mm. 10 Process for the production of polyester fibers and filaments stabilized with carbodiimides, characterized in that at most a stoichiometric amount of mono- and / or biscarbodiimide, and at least 0.15% by weight, based on the polyester, of A polycarbodiimide is added to the polyester prior to spinning, after which it is spun into yarn in known manner. 9. A process according to claim 8, characterized in that less than 90% of the stoichiometric required amount, preferably only 50-85% of this amount is added as mono- and / or biscarbodiimide. Method according to claim 8 or 9, characterized in that the polyester spun without carbodiimide additive has after the spinning carboxyl groups corresponding to the stoichiometric required: the amount of mono- or bicarbodiimides less than 20, preferably less than 10 moles / kg of polyester. Method according to any of claims 8 to 10, characterized in that the contact time of the molten polyester and the added carbodiimide is less than 5, preferably less than 3 minutes. ! Method according to any of claims 8 to 11, characterized in that the average molecular weight of the polyester to be processed corresponds to at least an intrinsic viscosity of 0.64 (dl / g) measured in dichloroacetic acid at 25 ° C. 103812 Process according to any one of claims 8 to 12, characterized in that the polycarbodiimi is added to the polyester to be processed, as a concentrate in a polymer, preferably polyester. 5 Process according to any one of claims 8 13, characterized in that the carbodiimide is added immediately before the spin of the polyester in an extruder or before an extruder. Process according to any one of claims 8 to 10, characterized in that N, N'-2,6,2 ', 6'-tetraisopropyldiphenylcarbodiimide is used as monocarbodiimide. Process according to any one of claims 8 to 15, characterized in that, as a polycarbodiimide, an aromatic polycarbodiimide in which the benz ring is substituted with an isopropyl group in the o-position relative to the carbodiimide group, i.e. in the 2.6 or 2.4.6 position. Use of filaments according to any of claims 1-7 for the production of paper machine wires. 20